Yousong -
As a side note to your side note - If you examine the actual mechanics of the allocation, the memory block is indeed size aligned to
(4*sizeof(size_t)), but the actual pointer returned is offset of (2*sizeof(size_t)) within the block. As in CHUNK_TO_MEM...
Peace,
/ted (sorry for the top-post)
-----Original Message-----
From: Yousong Zhou
Sent: Thursday, February 23, 2017 8:07 PM
To: Ted Hess
Cc: lede-dev
Subject: Re: [LEDE-DEV] [PATCH] libubox: Fix calloc_a() to return mem aligned
pointers
On 24 February 2017 at 08:30, Ted Hess <th...@kitschensync.net> wrote:
-----Original Message----- From: Yousong Zhou
Sent: Thursday, February 23, 2017 7:15 PM
To: Ted Hess
Cc: lede-dev
Subject: Re: [LEDE-DEV] [PATCH] libubox: Fix calloc_a() to return mem
aligned pointers
On 24 February 2017 at 05:20, Ted Hess <th...@kitschensync.net> wrote:
The current implementation of calloc_a() returns packed pointers for the
extra
arguments. These packed, unaligned, pointers are OK for a lot of
architectures,
but not all. This patch will aligned the pointers returned in a manner
congruent
with malloc(). I do not believe the extra padding overhead is all the
burdensome
considering the overhead of separate malloc/calloc/free call to accomplish
the
same thing.
Signed-off-by: Ted Hess <th...@kitschensync.net>
---
utils.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/utils.c b/utils.c
index 5d9d5aa..314f716 100644
--- a/utils.c
+++ b/utils.c
@@ -27,6 +27,9 @@
_addr; \
_addr = va_arg(_arg, void **), _len = _addr ? va_arg(_arg,
size_t) : 0)
+#define C_PTR_ALIGN (2*sizeof(size_t))
+#define C_PTR_MASK (-C_PTR_ALIGN)
+
sizeof(long) should be used for C_PTR_ALIGN, though I cannot find the
quote at the moment...
yousong
I picked the expression from malloc in the musl sources. No hard
preferences, but it does do proper alignment for 64-bit systems and other
sensitive data-types AFAICT.
/ted
Okay, according to the c99, size_t is supposed be able to express
sizeof(char[LONG_MAX]). So I guess your code is safer than
sizeof(long) actually ;)
But as a side note, at the moment, musl malloc uses (4*sizeof(size_t))
as SIZE_ALIGN, uClibc uses (2 * (sizeof(size_t))) as MALLOC_ALIGNMENT
yousong
_______________________________________________
Lede-dev mailing list
Lede-dev@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/lede-dev
